Noise Rating

Noise Rating (NR) is a single-number descriptor derived from the NR curve system, representing the maximum NR curve exceeded by a measured octave-band noise spectrum. A measured spectrum is plotted against the family of NR curves (ISO 1996), and the NR value equals the highest curve touched by any octave band. This means the rating is governed by the worst-performing frequency band. NR values are used in building services design (HVAC noise targets), background noise specifications, and environmental noise assessment. Common targets include NR 25 for classrooms and auditoria, NR 30 for general offices, NR 35 for retail spaces, and NR 40–45 for industrial offices. NR is the default noise criterion in the UK (BS 8233:2014), Singapore, Hong Kong, and many other countries. It provides more nuanced assessment than dB(A) alone because it evaluates the full frequency spectrum against a shaped criterion reflecting human sensitivity.